Polyimides are widely used in the manufacture of electronic components as a film-forming resin possessing excellent electrical, mechanical, chemical and thermal characteristics. Each particular use has its particular physical and chemical requirements. However, in many cases the polyimide required for the application has limited or no solubility in the solvents acceptable for applying the polyimide films. Numerous highly polar solvents are not acceptable for film casting due to safety or boiling point issues, so solubility in moderate polarity solvents is required. As a result, many of the coatings are cast as the somewhat more solvent soluble polyamic acid film and then cured at high temperatures. This may result in some damage to the substrate/device and the equipment employed in the high temperature cure. Furthermore, the dehydration of the polyamic acid to polyimide shrinks the film by approximately 15-20%, which frequently increases the stress on the film, and thus the underlying substrate/device.
The growth of Inkjet technology for various coating applications has been strong. Particular advantages include the lowering the amount of coating solution required, and the ability to coat in specific areas, which can reduce the need for lithographic patterning steps. However, in order to reproducibly manufacture semiconductor devices, certain requirements must be met, such as excellent patternability, storage stability, minimal number of applications to obtain desired film thickness, low tendency to clog the tiny inkjet nozzles even with long delays between jetting uses, compatibility with the inkjet head, and uniform droplet formation. Prior art polyamic acids and polyimides tend to have low solubility in common inkjet solvents, which results in poor drop formation, inferior storage stability, and significant clogging of the inkjet nozzles.
Thus, there is a need for thermosetting compositions employing polyimide polymers highly soluble in moderate polarity solvents for various applications. The present disclosure describes a highly soluble class of polyimide polymers and their novel thermosetting compositions suitable for use in microelectronic applications. Compositions of the present disclosure are particularly suitable for deposition using inkjet printing due to their high solubility, excellent storage stability, and low clogging of inkjet nozzles.